In actio optophysiological analyses reveal functional diversification of dopaminergic neurons in the nematode C. elegans

Abstract

Many neuronal groups such as dopamine-releasing (dopaminergic) neurons are functionally divergent, although the details of such divergence are not well understood. Dopamine in the nematode Caenorhabditis elegans modulates various neural functions and is released from four left-right pairs of neurons. The terminal identities of these dopaminergic neurons are regulated by the same genetic program, and previous studies have suggested that they are functionally redundant. In this study, however, we show functional divergence within the dopaminergic neurons of C. elegans. Because dopaminergic neurons of the animals were supposedly activated by mechanical stimulus upon entry into a lawn of their food bacteria, we developed a novel integrated microscope system that can auto-track a freely-moving (in actio) C. elegans to individually monitor and stimulate the neuronal activities of multiple neurons. We found that only head-dorsal pair of dopaminergic neurons (CEPD), but not head-ventral or posterior pairs, were preferentially activated upon food entry. In addition, the optogenetic activation of CEPD neurons alone exhibited effects similar to those observed upon food entry. Thus, our results demonstrated functional divergence in the genetically similar dopaminergic neurons, which may provide a new entry point toward understanding functional diversity of neurons beyond genetic terminal identification.

Calcium dynamics regulating the timing of decision-making in C. elegans

“…We integrated the OSB system, an auto-tracking microscope system for calcium imaging and optogenetic analyses of neuronal activity in C. elegans (Video 2), with an odor-delivery sub-system (Busch et al, 2012; Tanimoto et al, 2016). Using this new OSB2 system, a moving C. elegans was continuously exposed to an odor flowing from syringe pumps (Figure 3A and Figure 3—figure supplement 1A, and Video 3).…”

“…For the OOSaCaBeN ( O lfactory and O ptogenetic S timulation a ssociated with Ca lcium imaging on Be having N ematode, or OSB2) system, we integrated an auto-tracking microscope system for calcium imaging and optogenetic manipulation with an odor-delivery subsystem (Busch et al, 2012; Tanimoto et al, 2016). Briefly, a wild-type C. elegans (N2) on a NGM plate was placed on a motorized stage HV-STU02 (HawkVision, Japan) combined with an upright microscope and illuminated with infrared light.…”

“…The details of calcium imaging with the OSB system were previously described (Tanimoto et al, 2016). In brief, the sample was exposed to excitation light from a MiLSS (Multi-independent Light Stimulation System, Aska Company, Japan) (Sakai et al, 2013).…”

Whole-organism behavioral profiling reveals a role for dopamine in state-dependent motor program coupling inC. elegans

“…Thus, we analyzed the velocity changes Animals have dramatically lower egg-laying rates when they are removed from their food source. Because dopamine signaling is thought to be elevated in the presence of food (Sawin et al, 2000;Tanimoto et al, 2016), we asked whether increasing dopaminergic neuron activity in the absence of food was sufficient to increase egg-laying rates. Strikingly, we found that activation of dat-1::CoChR could drive animals to lay eggs in the absence of food at significantly higher rates (Figure 4E-F; velocity in Figure 4figure supplement 1B).…”

Dopaminergic neurons modulate locomotion inCaenorhabditis elegans

“…Dopamine is responsible for a spectrum of behaviours. It has been shown that it is responsible for slowing of locomotion on the encounter of food [42][43][44][45][46][47] , in local search behaviour along with serotonin 43 , and in learning and decision making [48][49][50] . Dopaminergic neurons are known to be mechanosensory 20,28,42,43,[51][52][53] that have been shown to respond to harsh touch stimulation [54][55][56] with ADE responsible for anterior touch sensation and PDE responsible for its posterior counterparts [57][58][59] .…”